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Odour Source
Overview
A location or object that emanates odours. Sources can be divided by point, area, or volume sources that are of either passive, active or fugitive type. For example, a rectangular oil pond would be labelled as a ‘passive area source’ and a biofilter may be labelled as an ‘active area source.’ The term diffuse source is used to describe area or volume sources. Fugitive samples are essentially unintended releases of odour. A summary is shown below:
Point source > Passive or active or fugitive
Diffuse source > Area source or volume source > Passive or active or fugitive
Classifying by Geometry
The three source geometries describe how emissions leave the source:
- Point Source – emission from a single, small opening, such as a stack
- Diffuse Source – a defined area or volume without controlled airflow, such as a waste dump or compost pile
- Volume Source – a three-dimensional structure with many emission points, such as a building
Classifying by Flow Behaviour
Sources are also classified by whether their airflow is controlled, using the VDI 3880 threshold of 30 m/h:
- Passive Source – no defined flow or a weak flow, under 30 m/h, such as a pond or waste dump
- Active Source – a defined gas flow of 30 m/h or greater, such as a biofilter or aerated pond
Classifying by Intent
A separate axis captures whether the release was intended:
- Fugitive Source – an unintended release with no fixed time or concentration, such as a door opening at a waste transfer station
- Fugitive Release – the unintended emission itself, from equipment such as flanges, valves, doors, or windows
How They Combine in Practice
These classifications are not mutually exclusive; a single source is usually described along all three axes at once. An oil pond is a diffuse, passive source. A stack is a point source, typically sampled as an active source. A leaking valve is a fugitive release, and the broader unintended-emission pattern from that equipment would be described as a fugitive source.